Fiber composite system and method for pipe reinforcement

ABSTRACT

A reinforced pipe and a method of preparing the reinforced pipe are provided. The reinforced pipe has repair area where a wrinkle bend is present in a center section of the repair area. The reinforced pipe comprises a unidirectional fabric circumferentially wrapped around the repair area of the pipe so as to result in multiple layers of the unidirectional fabric around the repair area. The unidirectional fabric is composed of high-performance fibers with at least 90% of the high-performance fibers oriented in the 90° direction, and the unidirectional fabric is wrapped such that the high-performance fibers run in the axial direction. The reinforced pipe further comprises a bidirectional fabric wrapped of over the unidirectional fabric such the at least one layer of bidirectional fabric is wrapped over the unidirectional fabric.

RELATED APPLICATIONS

This application claims priority to U.S. provisional application Ser.No. 62/471,232, filed Mar. 14, 2017, which is incorporated by referenceherein in its entirety.

FIELD

The present disclosure relates generally to pipe reinforcement andrepairs, and more specifically, to reinforcing or repairing pipes byusing composite fiber materials.

BACKGROUND

Defects in steel pipes utilized in pipelines can result in fatigue andfailure of the pipe when the pipe undergoes stress such as can occurduring the transportation of hydrocarbon compounds, such as oil andnatural gas. For a steel pipe with corrosion, dents, gouges and/orcracks, the primary stress in the pipe is exerted in the hoop direction.Therefore, common composite reinforcement or repair systems have beendirected to reducing these hoop stresses on the pipe thus preventingfatigue and failure. However, in a wrinkle bend, the most common failureoccurs due to high amounts of strain in the axial direction of the pipe.Traditional composite reinforcement systems have not been able toadequately reinforce the pipes at wrinkle bends when installed usingtraditional application techniques.

Wrinkle bends are introduced in a pipe during construction; typically,they are introduced during alignment of the pipe by bending. Bendingpractices used during pipeline construction often resulted incircumferential pipe deformation or wrinkles on the inside bend radiusof the pipe. Vintage wrinkle bends are often of the wave shape withoutward deformations. Additionally, “mild ripples” are those developedusing modern day field-bending techniques where such ripples bear alength to height ratio on the order of 12. Whereas the wrinkle bendsfound typically on vintage built pipelines are sharper than theseripples with length to height ratio on the order of 4.

SUMMARY

In accordance with one series of embodiments of the current disclosure,there is provided a reinforced pipe having an axial direction and acircumferential direction with a wrinkle bend oriented in thecircumferential direction. The pipe comprises a repair area having aleft section, a right section and a center section such that the centersection is between the left section and the right section. The centersection contains the wrinkle bend.

The pipe further comprises a unidirectional fabric (specifically wovento provide all or most of the yarn in the weft direction)circumferentially wrapped around the repair area of the pipe so as toresult in multiple layers of the unidirectional fabric around the repairarea. The unidirectional fabric has a length, a width, a 0° directioncorresponding to the length and a 90° direction corresponding to thewidth. The unidirectional fabric is composed of high-performance fiberswith at least 90% of the high-performance fibers oriented in the 90°direction, and the unidirectional fabric is wrapped such that thehigh-performance fibers run in the axial direction.

The pipe also comprises a bidirectional fabric wrapped over theunidirectional fabric such that at least one layer of bidirectionalfabric is wrapped over the unidirectional fabric. The layers ofunidirectional fabric and layers of bidirectional fabric make up thetotal layers of fabric around the repair areas. The unidirectionalfabric makes up at least 70% of the total layers of fabric at the centersection. The unidirectional fabric and bidirectional fabric can bewrapped wet with epoxy resin.

In some embodiments, the unidirectional fabric can make up at least 60%of the total layers of fabric at the left edge section and make up atleast 60% of the total layers of fabric at the right edge section. Thebidirectional fabric can make up at least 20% of the total layers offabric at the left edge section and make up at least 20% of the totallayers of fabric at the right edge section. In some of theseembodiments, the unidirectional fabric can make up at least 75% of thetotal layers of fabric at the center section. The unidirectional fabriccan make up at least 65% of the total layers of fabric at the left edgesection and make up at least 65% of the total layers of fabric at theright edge section. The bidirectional fabric can make up at least 30% ofthe total layers of fabric at the left edge section and make up at least30% of the total layers of fabric at the right edge section. Further,the unidirectional fabric can make up at least 80% of the total layersof fabric at the center section.

In some embodiments, the unidirectional fabric is wrapped around therepair area in multiple strips and each strip is of sufficient lengthsuch that each strip provides at least one layer, and many times twolayers when wrapped circumferentially around the pipe. Additionally,every other strip of the unidirectional fabric is offset from thepreceding layer by from 40% to 60% of the width of the unidirectionalfabric. In some cases, the offset can be about 50% of the width of theunidirectional fabric. Also, the bidirectional fabric can be wrapped soas to have a similar offset.

In some embodiments, the unidirectional fabric is composed ofhigh-performance fibers and conventional fibers with thehigh-performance fibers oriented in the 90° direction and theconventional fibers oriented in the 0° direction, and the conventionalfibers are stitched to the high-performance fibers thus holding them inthe 90° direction. Typically, the high-performance fibers can have aYoung's modulus of at least 100 GPa and a tensile strength of at least1300 MPa based on a fiber diameter of 8 μm to 20 μm. The conventionalfibers can have a Young's modulus of less than 50 GPa and a tensilestrength of less than 1100 MPa based on a fiber diameter of from 8 μm to20 μm.

In some embodiments, the bidirectional fabric has a length, a width, a0° direction corresponding to the length of the bidirectional fabric anda 90° direction corresponding to the width of the bidirectional fabric.The bidirectional fabric can have from 35% to 75% of its fiber runningin the 0° direction of the bidirectional fabric and 35% to 75% of itsfiber running in the 90° direction of the bidirectional fabric.

In accordance with another series of embodiments of the currentdisclosure, there is provided a method of reinforcing a pipe inaccordance with the above embodiments. The pipe has an axial directionand a circumferential direction with a wrinkle bend oriented in thecircumferential direction. The method includes applying a load transfermaterial in a repair area of the pipe around the wrinkle bend so as toprovide a smooth transition. The repair area has a left section, a rightsection and center section such that the center section is between theleft section and right section and contains the wrinkle bend. The methodfurther includes applying a resin over the repair area, and wrappingmultiple layers of a unidirectional fabric circumferentially around therepair area. The unidirectional fabric has a length, a width, a 0°direction corresponding to the length and a 90° direction correspondingto the width. The unidirectional fabric is composed of high-performancefibers with 90% of the high-performance fibers oriented in the 90°direction. The unidirectional fabric is wrapped such that thehigh-performance fibers run in the axial direction. The method alsoincludes wrapping at least one layer of a bidirectional fabric over theunidirectional fabric such that the layers of unidirectional fabric andlayers of bidirectional fabric make up the total layers of fabric aroundthe repair area, and wherein the unidirectional fabric makes up at least70% of the total layers of fabric at the center section.

In some embodiments, the unidirectional fabric is wrapped around therepair area in multiple strips and each strip is of sufficient lengthsuch that each strip provides at least two layers when wrappedcircumferentially around the pipe. Every other strip of theunidirectional fabric can offset from the preceding layer by from 40% to60% of the width of the unidirectional fabric or by about 50% of thewidth of the unidirectional fabric.

In some embodiments, the method further comprises applying the resin tothe unidirectional fabric and bidirectional fabric prior to wrapping theunidirectional fabric or bidirectional fabric around the pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a pipe having a wrinkle bend.

FIG. 2 is a perspective view of the pipe of FIG. 1 with a resin coatingon the repair area.

FIG. 3 is a perspective view of the pipe of FIG. 2 illustrating theapplication of a unidirectional fabric to the repair area.

FIG. 4 is a perspective view of the pipe of FIG. 3 illustrating thecompleted application of the unidirectional fabric.

FIG. 5 is a perspective view of the pipe of FIG. 4 illustrating theapplication of a bidirectional fabric to the repair area.

FIG. 6 is a perspective view of the pipe of FIG. 5 illustrating thecompleted application of the bidirectional fabric.

FIG. 7 is an illustration of a unidirectional fabric for use in thereinforcement of a pipe in accordance with this disclosure.

FIG. 8 is a graph of stress v. strain that illustrates the stress andstrain ranges for a typical bending cycle for Control I, Control II,Control III and Example I.

DETAILED DESCRIPTION

In the description that follows, like parts are marked throughout thespecification and drawings with the same reference numerals,respectively. The drawings are not necessarily to scale and theproportions of certain parts have been exaggerated to better illustratedetails and features of the invention. In the following description, theterms “inwardly” and “outwardly” are directions toward and away from,respectively, the geometric axis of a referenced object. Wherecomponents of relatively well-known designs are employed, theirstructure and operation will not be described in detail.

Referring now to FIG. 1, a pipe 10 is illustrated. Pipe 10 is a pipehaving a wrinkle bend 12. Typically, pipe 10 will be a metal pipe, suchas steel, aluminum, etc. More typically, pipe 10 is a steel pipe.Wrinkle bend 12 is the type that is introduced in a pipe duringconstruction during alignment of the pipe by bending. Wrinkle bend 12runs circumferentially along pipe 10. A repair area 14 is defined aroundwrinkle bend 12. The repair area has a left section 16, a center section18 and a right section 20. Center section 18 is between left section 16and right section 20, and center section 18 contains wrinkle bend 12.Pipe 10 has an axial direction (or longitudinal direction) 22 and acircumferential direction 24. As previously indicated, wrinkle bend 12is oriented in the circumferential direction.

In accordance with this disclosure, there is provided a reinforced pipewherein the pipe 10 has wrinkle bend 12, and repair area 14 around thewrinkle bend has been reinforced by several distinct layers. Thereinforced pipe is described below in relation to FIGS. 2 to 6, whichillustrate the distinct layers.

Turning now to FIG. 2, the first layer to be deposited on pipe 10typically will be a load transfer material 26 to even out the surface ofthe repair area and fill in any gaps or voids in the surface, such asdents, gouges and/or cracks. The load transfer material typically istested for compressive strength and modulus, and additionally forcompatibility with the composite system being applied to the pipe 10.While generic load transfer materials are often unsuitable for use inthis application, the load transfer material generally can be anysuitable putty such as epoxy putties designed for making fast andcurable repairs to metals, or ceramic load transfer fillers. Loadtransfer material 26 is applied to center section 18, in the location ofthe wrinkle bend, and in localized areas within repair section 14 whereany other defects may exist.

In some embodiments, a resin is applied on top of load transfer material26, generally before the load transfer material has cured. In suchembodiments, resins are applied in an uncured or partially cured stateand at least the unidirectional fabric (see discussion below) is appliedprior to the resin curing. The resin can be configured to cure into arigid or semi-rigid state after the unidirectional fabric is applied.Some non-limiting examples of resins used to adhere adjacentunidirectional fibers and to adhere overlying unidirectional fiberlayers include polyurethane, polyurea, epoxy, polyimide,polyoxazolidones, silanes, vinyl ester resins, and/or any one, two, ormulticomponent resin systems. In some aspects, the resins include apolyurethane material having an aliphatic prepolymer. In some aspects,the resins can include a polyurethane material having an aliphaticisocyanate prepolymer. In some aspects, the resins can include apolyurethane material having an isocyanate prepolymer. In some aspects,the resins (e.g., one with an aliphatic isocyante prepolymer) include apolyurethane material chemically configured to activate and harden afterremoval from a generally inert environment and exposure to humid air,moisture-borne air, or an environment that otherwise provided moistureto activate the resin. In some embodiments, the resins include atwo-part bisphenol epoxy resin material having a modified aliphaticamine hardener. The resins can also include a two-part novolac epoxyresin material having a modified aliphatic amine hardener.

As illustrated in FIGS. 3 and 4, a unidirectional fabric 28 is placed ontop of load transfer material 26 and resin, if applied. Unidirectionalfabric 28 is circumferentially wrapped around repair area 14 of the pipeso as to result in multiple layers of the unidirectional fabric aroundrepair area 14.

The unidirectional fabric used in the current disclosure is one withhigh-performance fibers, which are oriented in a direction so that thehigh-performance fibers will be aligned in the axial direction when thefabric is applied to the pipe. Generally, the unidirectional fabric isone specifically woven to provide all or most of the yarn in the weftdirection.

Referring to FIG. 7, unidirectional fabric 28 has a length 30 and width32, with length 30 typically being greater than width 32. Often, width32 will be less than the pipe circumference, and length 30 will begreater than the pipe circumference and even greater than two pipecircumferences. The length corresponds to the 0° direction for thefabric and the width corresponds to the 90° direction of the fabric.Unidirectional fabric 28 will have substantially all of itshigh-performance fibers 34 oriented in the 90° direction. Generally,this will mean that at least 90% of high-performance fibers 34 areoriented in the 90° direction. Typically, at least 95% or at least 98%of high-performance fibers 34 are oriented in the 90° direction. Moretypically, at least 99%, at least 99.5%, at least 99.9% or 100% ofhigh-performance fibers 34 are oriented in the 90° direction.

In one embodiment, the unidirectional fabric is made of high-performancefibers 34 oriented in the 90° direction and conventional fibers 36oriented in the 0° direction. Conventional fibers 36 are stitched tohigh-performance fibers 34 to thus hold them in the 90° direction.Generally, in such embodiments the conventional fibers 36 are present inonly the amount necessary to ensure that the high-performance fibers 34remain oriented in the 90° direction. Thus, the conventional fiberstypically make up less than 2%, less than 1%, less than 0.5% or lessthan 0.1% of the total fibers (conventional fibers plus high-performancefibers) present in the fabric.

Generally, high-performance fibers are those that are engineered forspecific uses that require exceptional strength, stiffness, heatresistance, or chemical resistance. These fibers have generally highertenacity and higher modulus than typical fibers. As used herein,high-performance fibers having a Young's modulus of at least 50 GPa anda tensile strength of at least 1100 MPa based on a fiber diameter offrom 8 μm to 20 μm at ambient temperature and pressure. Typically, thehigh-performance fibers used herein have a Young's modulus of at least100 GPa and a tensile strength of at least 1300 MPa based on a fiberdiameter of from 8 μm to 20 μm. More typically, the Young's modulus willbe at least 150 GPa or at least 200 GPa, and the tensile strength willbe at least 1500 MPa or at least 2000 MPa for a fiber diameter of from 8μm to 20 μm. Non-limiting examples of high-performance fibers useful inthe unidirectional fabric include carbon fibers (both pan and pitchbased), glass fibers, ceramic fibers, basalt fibers and metal fibers.Currently, carbon fibers and glass fibers are preferred. Typically, thehigh-performance fibers will be carbon fibers or glass fibers.

On the other hand, conventional fibers, as used herein, are fibershaving a Young's modulus of less than 50 GPa and a tensile strength ofless than 1100 MPa based on a fiber diameter of from 8 μm to 20 μm atambient temperature and pressure. More typically, the Young's moduluswill be less than 40 GPa or less than 30 GPa, and the tensile strengthwill be less than 1000 MPa or less than 900 MPa for a fiber diameter offrom 8 μm to 20 μm. Non-limiting examples of conventional fibers includecotton fibers, rayon fibers, polyester fibers and wool.

As illustrated in FIG. 3, the unidirectional fabric is wrapped aroundpipe 10 such that the 90° direction of the fabric runs parallel to axialdirection 22 of pipe 10. Accordingly, when the unidirectional fabric isapplied to pipe 10, the high-performance fibers run in the axialdirection.

Generally, the unidirectional fabric will be applied in strips 38 (shownas 38 a and 38 b) of a length sufficient to wrap at least once aroundthe circumference of repair area 14 of pipe 10. Typically, strips 38will be of a length sufficient to wrap at least twice around thecircumference of repair area 14 of pipe 10. In most applications, thelength of a strip 38 will only be sufficient to provide two layers ofunidirectional fabric around pipe 10. Accordingly, multiple strips areused to wrap the repair areas. In one embodiment, every other strip ofthe unidirectional fabric is offset from the preceding layer by from 40%to 60% of the width of the unidirectional fabric, and typically, about50% of the width of the unidirectional fabric. For example, a firststrip 38 a can be wrapped to form two layers in center section 18 ofrepair area 14 over wrinkle bend 12. Next, a second strip 38 b can bewrapped to overlap about 50% of the width of first strip 38 a. With aportion of second strip 38 b extending to the right of first strip 38 a.Additional overlapping strips can be wrapped extending farther rightuntil the right edge 40 of right section 20 is reached. Similarly,strips of unidirectional fabric can be wrapped overlapping first strip38 b to the left until the left edge 42 of left section 16 is reached.As will be realized, this will result in center section 18 having fourlayers of unidirectional fabric (two layers per each strip); however, atright edge 40 and left edge 42 there will be only two layers ofunidirectional fabric. Generally, multiple wraps at each section will beperformed so as to build up several unidirectional layers in centersection 18, typically 10 or more, 12 or more or 20 or more layers. Thenumbers of layers can be reduced towards the edges so that the number oflayers at the edges is less than the number of layers at center section18. In some applications, the number of layers at right edge 40 and leftedge 42 will be half or less than half the layers at center section 18and can be a third or less of the number of layers.

In many embodiments, the unidirectional fabric will be applied wet withresin. That is, the unidirectional fabric will be coated with an uncuredresin prior to application of the unidirectional fabric to pipe 10.Generally, the uncured resin will be applied on site just beforeapplication of the unidirectional fabric to pipe 10. In suchembodiments, the resins initially can be in an uncured or partiallycured state prior to the unidirectional fabric being applied to the pipefor reinforcement. Then the resin can be configured to cure subsequentlyinto a rigid or semi-rigid state after the unidirectional fabric hasbeen applied to the pipe, more typically, after the bidirectional fabrichas been applied, as described below. In this manner, the unidirectionalfabric layers are non-mechanically connected using the resinous materialthat adheres the unidirectional fabric layers to each other.

Some non-limiting examples of resins used to adhere adjacentunidirectional fibers and to adhere overlying unidirectional fiberlayers include polyurethane, polyurea, epoxy, polyimide,polyoxazolidones, silanes, vinyl ester resins, and/or any one, two, ormulticomponent resin systems. In some aspects, the resins include apolyurethane material having an aliphatic prepolymer. In some aspects,the resins can include a polyurethane material having an aliphaticisocyanate prepolymer. In some aspects, the resins can include apolyurethane material having an isocyanate prepolymer. In some aspects,the resins (e.g., one with an aliphatic isocyante prepolymer) include apolyurethane material chemically configured to activate and harden afterremoval from a generally inert environment and exposure to humid air,moisture-borne air, or an environment that otherwise provided moistureto activate the resin. In some embodiments, the resins include atwo-part bisphenol epoxy resin material having a modified aliphaticamine hardener. The resins can also include a two-part novolac epoxyresin material having a modified aliphatic amine hardener.

Turning now to FIGS. 5 and 6, a bidirectional fabric 44 is placed on topof unidirectional fabric 28. Bidirectional fabric 44 iscircumferentially wrapped around repair area 14 of the pipe so as toresult in multiple layers of the bidirectional fabric around repair area14.

The bidirectional fabric used in the current disclosure is one withhigh-performance fibers, which are oriented in a direction so that aportion of the high-performance fibers will be aligned in the axialdirection and a portion of the high-performance fibers will be alignedin the circumferential direction when the fabric is applied to the pipe.Accordingly, the bidirectional fabric 44 will have a portion of itshigh-performance fibers 46 oriented in the 90° direction (width) and aportion oriented in the 0° direction (length). Generally, thebidirectional fabric has from 35% to 75% of its fiber running in the 0°direction of the bidirectional fabric and 35% to 75% of its fiberrunning in the 90° direction of the bidirectional fabric. Typically,about 50% of the fibers will run in the 0° direction and about 50% ofthe fibers will run in the 90° direction. The bidirectional fabric canbe a woven fabric.

Generally, the bidirectional fabric 44 can be applied in strips (e.g.,44 a, 44 b) similar to the description above for the unidirectionalfabric. Typically, the bidirectional fabric 44 will be applied wet withresin as described for the unidirectional fabric 28.

Multiple layers of the bidirectional fabric 44 can be applied to therepair area 14. The layers of unidirectional fabric 28 and layers ofbidirectional fabric 44 make up the total layers of fabric around therepair area 14. Generally, the unidirectional fabric 28 makes up atleast 70% of the total layers of fabric at the center section 18.Typically, the unidirectional fabric 28 makes up at least 60% of thetotal layers of fabric at the left edge section 16 and makes up at least60% of the total layers of fabric at the right edge section 20, and thebidirectional fabric 44 makes up at least 20% of the total layers offabric at the left edge section 16 and makes up at least 20% of thetotal layers of fabric at the right edge section 20. In someembodiments, the unidirectional fabric 28 makes up at least 75% of thetotal layers of fabric at the center section 18, the unidirectionalfabric 28 makes up at least 65% of the total layers of fabric at theleft edge section 16 and makes up at least 65% of the total layers offabric at the right edge section 20, and the bidirectional fabric 44makes up at least 30% of the total layers of fabric at the left edgesection 16 and makes up at least 30% of the total layers of fabric atthe right edge section 20. Additionally, the unidirectional fabric 28can make up at least 80% of the total layers of fabric at the centersection 18.

In most embodiments, at the repair area 14, the reinforced pipecomprises the bidirectional fabric 44 wrapped directly onto theunidirectional fabric 28 without any other fabric or fiber materialin-between the unidirectional fabric 28 and the bidirectional fabric 44.Additionally, in these embodiments the unidirectional fabric 28 iswrapped directly onto the pipe 10, which includes being wrapped directlyonto the load transfer material 26 and/or resin where those are used. Inother words, the unidirectional fabric 28 is wrapped onto the pipe 10without any other fabric or fiber material in-between the pipe 10 andthe unidirectional fabric 28. In some embodiments, the repair area 14consists essentially of resin-impregnated bidirectional fabric 44wrapped on the resin-impregnated unidirectional fabric 28, which iswrapped over the filler material 24, resin (if used) and pipe 10.

The above-reinforced pipe 10 can be produced by a method wherein thesurface of the repair area 14 is prepared to receive the reinforcingfabrics, i.e., the unidirectional and bidirectional fabrics 28, 44. Forexample, the load transfer material 26 is first applied on a repair area14 of the pipe 10 around the wrinkle bend 12 so as to provide a smoothtransition across the repair area 14 and to cover any dents, cracks, orsimilar defects in the pipe 10. Typically, the load transfer material 26is not allowed to cure before further layers are added to the repairarea 14.

Also, the resin can be coated onto the repair area 14. Generally, theresin is coated onto the uncured load transfer material 26, if used. Theresin is typically applied in an uncured state and generally will beallowed to cure after application of the unidirectional fabric 28 and,in some cases, after application of the unidirectional fabric 28 and thebidirectional fabric 44.

After the surface of the pipe 10 in the repair area 14 has beenprepared, multiple layers of the unidirectional fabric 28 can be wrappedcircumferentially around the repair area 14. As indicated above, theunidirectional fabric 28 is wrapped such that the high-performancefibers 34 run in the axial direction 22. For sufficient coverage andsecure application, each strip 38 of unidirectional fabric 28 usedshould be at least equal to the circumference of the pipe 10 in length(0° direction). More typically, the fabric length will be greater thanor equal to a least twice the circumference of the pipe 10.

After the unidirectional fabric 28 has been wrapped to completely coverthe repair area 14—typically with multiple fabric layers—thebidirectional fabric 44 is wrapped over the unidirectional fabric 28such that the layers of unidirectional fabric 28 are covered by thebidirectional fabric 44. Generally, the bidirectional fabric 44 willentirely cover the unidirectional fabric 28 and will be applied instrips (e.g., 44 a, 44 b) with each strip of bidirectional fabric 44 atleast equal to the circumference of the pipe 10 in length (0°direction). More typically, the bidirectional fabric length will begreater than or equal to a least twice the circumference of the pipe 10.Generally, there will be multiple layers of bidirectional fabric 44 overthe repair area 14, as described above. In presently preferredembodiments, the layers of bidirectional fabric 44 and unidirectionalfabric 28 are not intermixed. That is, there is no alternating of thelayers of bidirectional fabric and unidirectional fabric; rather, allthe unidirectional fabric layers are applied first and then thebidirectional fabric layers are applied.

Typically, the method will comprise applying the resin to eachunidirectional fabric strip 38 a, 38 b and each bidirectional fabricstrip 44 a, 44 b prior to wrapping the unidirectional fabric 28 orbidirectional fabric 44 around the pipe 10 so that each fabric strip iswrapped around the pipe 10 with the resin in an uncured state or “resinwet” state.

EXAMPLES

The structures and techniques described above are further illustrated bythe following examples, which are given by way of example only andshould not be taken as limiting of the present disclosure in any way.

Finite Element Analysis

Prophetic examples were calculated wherein pipe performance wasdetermined using finite element analysis (FEA). Performance is simulatedfor the following four scenarios.

-   -   Control I: A pipe free of all defects.    -   Control II: An unreinforced pipe having a wrinkle bend; that is,        a pipe utilizing no repair of the wrinkle bend defect.    -   Control III: A pipe having a wrinkle bend which is reinforced in        a conventional manner. A total composite thickness of        0.35-inches (8.9 mm) is simulated with all the fiber oriented in        the 0° fabric direction and axially on the pipe.    -   Example I: A pipe having a wrinkle bend which is reinforced in a        manner in accordance with this disclosure. The current composite        repair design discussed herein allows all pieces of fabric to be        installed in the hoop direction of the pipe (circumferentially        instead of axially), eliminating axial strips. A total composite        thickness of 0.43-inches (10.9 mm) is simulated with 0.34-inches        being unidirectional fiber oriented in the 90° fabric direction        and 0.09-inches being bidirectional fiber wrapped over the        unidirectional fiber.

Difference in composite thickness from Control III and Example Irepresent difference in design which resulted in different minimumthickness need to ensure ease of installation while still providing pipereinforcement.

An FEA is used to analyze the above scenarios. The FEA model is builtbased on the wrinkle bend geometry used in an experimental study onactual pipes. The pipe specifications for all the Examples herein matchthat of the prior study, which were 26-inch (650 mm) diameter by0.281-inch (7.14 mm) nominal wall thickness, Grade X52 carbon steel. Thewrinkle height (bulge above standard pipe surface) in the FEA simulationis 0.5-inches (12.7 mm) and the wrinkle length (extensioncircumferentially along the pipe) is 5 inches (127 mm). The FEA analysissimulates the pipe being pressurized internally to 810 psi (5.58 MPa),and then applying a bending moment range of +600 kip-ft (+82,953 kgf-m)to −400 kip-ft (−55,302 kgf-m) to the wrinkled pipe.

The FEA is performed on all four scenarios in two stages: an elasticsimulation to determine a theoretical stress concentration factor (SCF)and an elastic-plastic simulation to determine the strain range on thewrinkle of each scenario with respect to the bending moment range. Thedevelopment of the stress-strain response allows the prediction of thecyclic bending fatigue life of the two repair scenarios (Control III andExample I).

Elastic FEA Simulations

Elastic FEA is performed on the four scenarios noted above, with aninternal pressure of 810 psi (5.58 MPa) and a bending moment range of1,000 kip-ft (138,255 kgf-m). Table 1 shows the theoretical SCFscalculated using elastic FEA for Control II, Control III and Example I.Additionally, Table I shows the SCF that was calculated for aconventional wrinkle pipe repair as described for Control III but usinggathered strain gage data from a prior study (Control IV). The priorstudy was not a simulated study. The prior study utilized a 0.35-inches(8.9 mm) composite thickness, and failed after 749 bending cycles. Theinitial measured axial strain range at the wrinkle during the cyclingwas 4,997 με and the calculated stress concentration factor (SCF) was2.4.

TABLE 1 Elastic FEA Results Scenario SCF Control II 4.3 Control III 2.8Control IV 2.4 Example I 1.5

As seen in the elastic FEA results, the current design (Example I)lowers the theoretical stress concentration factor significantly andeven more so when compared to the unreinforced pipe with the wrinkle.Additionally, this analysis shows that the effective SCF measured usingstrain gages during the experimental study (Control IV) is close to theFEA-determined SCF. Therefore, the proximity of the results demonstratethat the FEA results were within the range of viability, and could betrusted to translate to increased performance on the full-scale testingor actual use.

Elastic-Plastic FEA Simulations

The elastic-plastic simulations on each of the four scenarios arecalculated to show the range of elastic and plastic deformation in thepipe and wrinkle under the varying repair methods. The elastic-plasticsimulations again use an internal pressure of 810 psi and a bendingmoment range of 1,000 kip-ft. Due to the high strain and plasticdeformation at the wrinkle section, low pressure cycle fatigue occursand leads to failure at the wrinkle location when unrepaired. Whenrepaired, the strain is reduced at the wrinkle, and therefore thefatigue life is extended. FIG. 8 shows the stress and strain ranges fora typical bending cycle for each of the four scenarios.

As seen in FIG. 8, both the stress and strain show the highest range onthe unrepaired wrinkled pipe (Control II). Control III (“Repair 1”) hasa slightly reduced stress range compared to Control II, whilesignificantly reducing the strain range. Meanwhile, Example I (“RepairII”) demonstrates a reduced stress and strain range over both Control IIand Control III, and therefore should shows an increase in bendingfatigue cycles. Example I most closely matches the stress and strangerange for a pipe with no defect (Control I).

The analysis shows the Example I design decreases the maximum strain atthe wrinkle by 69% in tension and 50% in compression when compared toControl III. Upon examination, the highest strains are found on theinside surface of the wrinkle.

The stress and strain range response presented in FIG. 8 for Control IIalso correlated closely with the actual strain gage data collected bySES during the prior study. Once again, the results of the FEA analysisare demonstrated to be accurate, and therefore it is predicted that theoptimized composite repair design will show increased bending fatigueresistance.

Sample Pipe Testing

Full-scale testing (non-prophetic) was performed on state-of-the-artequipment that can subject the required bending moments and internalpressures to a wrinkled 26-inch (650 mm) diameter pipe test samples.Strain gages were placed at strategic locations on and around thewrinkle to collect important information to evaluate strains, especiallythose measured on the reinforced samples that were used to quantify theperformance of each design.

Control V

To determine controlled baseline data, an unreinforced wrinkle wassubjected to the constant internal pressure of 810 psi and an 800 kip-ftrange of bending moments. Internal pressure was introduced and thespecimen was subjected to cycling between the minimum and maximumbending moments until failure resulted in the form of a leak. Thecontrol specimen failed within 165 bending cycles, due to a through-wallcircumferentially-oriented crack that had developed at the wrinkle.

Based on the results of the unrepaired wrinkle, a 1000 kip-ft bendingmoment range was chosen for the reinforced test specimens.

Examples

A first embodiment of the current design was installed on a wrinkledpipe as described for Example I. For Example II, the repair wasinstalled exactly as per Example I in the FEA analysis, providing a5-foot (1.5 m) composite repair length with a thickness of 0.43-inches(10.9 mm).

A second embodiment was installed on wrinkled pipe. For Example III, therepair was installed similarly to Example II with a composite repairlength of 5-feet (1.5 m), but increased the total composite repairthickness to 0.65-inches (16.5 mm). Layup configurations for Example IIand Example III are shown in Table 2.

TABLE 2 Example II and Example III: Composite Reinforcement LayupConfigurations Example II (0.43-inch Composite Example III (0.65-inchComposite Thickness) Thickness) 0.34-inches of proprietary fiber-0.56-inches of proprietary fiber- glass over the wrinkle and extend-glass over the wrinkle and extend- ing to a 5-foot repair length ing toa 5-foot repair length 0.09-inches of bi-directional 0.09-inches ofbi-directional carbon fiber over the 5-foot repair carbon fiber over the5-foot repair length length

Example II was pressurized to 810 psi and then subjected to the 1,000kip-ft bending moment range. Example II was subjected to 1,340 bendingcycles prior to composite failure. This represented an almost 600bending cycle increase compared to that determined for Control IV fromthe prior study. Additionally, the average axial strain range at thewrinkle was decreased from 4997 με for Control IV to approximately 4000με for Example II. The calculated SCF from the test was 1.8.

Example III was pressurized and then subjected to the 1,000 kip-ftbending moment range similar to the previous reinforced specimens.Example III finally failed at 2,068 bending cycles, a significantincrease compared to all previous iterations of the full-scaleexperiments. The axial strain range at the wrinkle also showedimprovement, decreasing to 3000 με and leading to a calculated SCF of1.2. This axial strain measurement and the resulting SCF were the lowestof all of the manufacturer's tested designs, demonstrating significantimprovement compared to Control IV and Example II. The results aresummarized in Table 3.

TABLE 3 Control IV (prior study) Example II Example III Bends Cycles to749 1,340 2,068 Failure Axial Strain Range 4,997με 4000με 3000με SCF 2.41.8 1.2

Overall, the FEA analysis closely mirrored the testing results that weregathered on full-scale pipe specimens. From both the FEA and full-scaletesting results, it can be seen that the current reinforcing system isan effective strategy for enhancing the fatigue resistance of thewrinkled pipes subjected to cyclic bending moments and constant internalpressure, as found in natural gas pipelines having wrinkle bends.Specifically, Example III decreased the axial strain at the wrinkle by40%.

The above Examples demonstrate, through FEA and full-scale testing, thatthe current system reduces the axial strain at the wrinkle, thereforeleading to an increased fatigue life. This increase in fatigue life canbe achieved by using the new fabric orientation of the currentembodiments that allow for reduction in installation error whileincreasing the speed and reliability of each installation. The optimizedcomposite repair system provides a safe repair alternative to largeenclosures or cut out and replacement. As a result, this currentcomposite repair system will save pipeline operators time and money byallowing for reduced material costs, installation times, and increasedreliability.

The above elements of the reinforced pipe and method as well as otherscan be seen with reference to the figures. From the above descriptionand figures, it will be seen that the present invention is well adaptedto carry out the ends and advantages mentioned, as well as thoseinherent therein. While the presently preferred embodiment of theapparatus has been shown for the purposes of this disclosure, thoseskilled in the art may make numerous changes in the arrangement andconstruction of parts. All of such changes are encompassed within thescope and spirit of the appended claims.

What is claimed is:
 1. A reinforced pipe having an axial direction and acircumferential direction with a wrinkle bend oriented in thecircumferential direction, the pipe comprising: a repair area having aleft section, a right section and a center section such that the centersection is between the left section and the right section, and thecenter section contains the wrinkle bend; a unidirectional fabriccircumferentially wrapped around the repair area of the pipe so as toresult in multiple layers of the unidirectional fabric around the repairarea; wherein the unidirectional fabric has a length, a width, a 0°direction corresponding to the length and a 90° direction correspondingto the width, and wherein the unidirectional fabric is composed ofhigh-performance fibers with at least 90% of the high-performance fibersoriented in the 90° direction, and wherein the unidirectional fabric iswrapped such that the high-performance fibers run in the axialdirection; and a bidirectional fabric wrapped over the unidirectionalfabric such that the at least one layer of bidirectional fabric iswrapped over the unidirectional fabric, and the layers of unidirectionalfabric and layers of bidirectional fabric make up the total layers offabric around the repair areas, and wherein the unidirectional fabricmakes up at least 70% of the total layers of fabric at the centersection.
 2. The reinforced pipe of claim 1, wherein the unidirectionalfabric and bidirectional fabric are wrapped wet with resin.
 3. Thereinforced pipe of claim 1, wherein the unidirectional fabric makes upat least 60% of the total layers of fabric at the left edge section andmakes up at least 60% of the total layers of fabric at the right edgesection, and wherein the bidirectional fabric makes up at least 20% ofthe total layers of fabric at the left edge section and makes up atleast 20% of the total layers of fabric at the right edge section. 4.The reinforced pipe of claim 3, wherein the unidirectional fabric makesup at least 75% of the total layers of fabric at the center section,wherein the unidirectional fabric makes up at least 65% of the totallayers of fabric at the left edge section and makes up at least 65% ofthe total layers of fabric at the right edge section, and wherein thebidirectional fabric makes up at least 30% of the total layers of fabricat the left edge section and makes up at least 30% of the total layersof fabric at the right edge section.
 5. The reinforced pipe of claim 4,wherein the unidirectional fabric makes up at least 80% of the totallayers of fabric at the center section.
 6. The reinforced pipe of claim1, wherein the unidirectional fabric is wrapped around the repair areain multiple strips and each strip is of sufficient length such that eachstrip provides at least two layers when wrapped circumferentially aroundthe pipe.
 7. The reinforced pipe of claim 6, wherein every other stripof the unidirectional fabric is offset from the preceding layer by from40% to 60% of the width of the unidirectional fabric.
 8. The reinforcedpipe of claim 1, wherein the unidirectional fabric is composed ofhigh-performance fibers and conventional fibers with thehigh-performance fibers oriented in the 90° direction and theconventional fibers oriented in the 0° direction, and wherein theconventional fibers are stitched to the high-performance fibers thusholding them in the 90° direction.
 9. The reinforced pipe of claim 8,wherein the high-performance fibers have a Young's modulus of at least100 GPa and a tensile strength of at least 1300 MPa based on a fiberdiameter of 8 μm to 20 μm.
 10. The reinforced pipe of claim 9, whereinthe conventional fibers have a Young's modulus of less than 50 GPa and atensile strength of less than 1100 MPa based on a fiber diameter of from8 μm to 20 μm.
 11. The reinforced pipe of claim 1, wherein thebidirectional fabric has a length, a width, a 0° direction correspondingto the length of the bidirectional fabric and a 90° directioncorresponding to the width of the bidirectional fabric, and wherein thebidirectional fabric has from 35% to 75% of its fiber running in the 0°direction of the bidirectional fabric and 35% to 75% of its fiberrunning in the 90° direction of the bidirectional fabric.
 12. A methodof reinforcing a steel pipe having an axial direction and acircumferential direction with a wrinkle bend oriented in thecircumferential direction, the method comprising: applying a loadtransfer material on a repair area of the pipe around the wrinkle bendso as to provide a smooth transition; wherein the repair area has a leftsection, a right section and center section such that the center sectionis between the left section and right section and contains the wrinklebend; applying a resin over the repair area; wrapping multiple layers ofa unidirectional fabric circumferentially around the repair area;wherein the unidirectional fabric has a length, a width, a 0° directioncorresponding to the length and a 90° direction corresponding to thewidth, and wherein the unidirectional fabric is composed ofhigh-performance fibers with 90% of the high-performance fibers orientedin the 90° direction, and wherein the unidirectional fabric is wrappedsuch that the high-performance fibers run in the axial direction;wrapping at least one layer of a bidirectional fabric over theunidirectional fabric such that the layers of unidirectional fabric andlayers of bidirectional fabric make up the total layers of fabric aroundthe repair area, and wherein the unidirectional fabric makes up at least70% of the total layers of fabric at the center section.
 13. The methodof claim 12, wherein the unidirectional fabric is wrapped around therepair area in multiple strips and each strip is of sufficient lengthsuch that each strip provides at least two layers when wrappedcircumferentially around the pipe.
 14. The method of claim 13, whereinevery other strip of the unidirectional fabric is offset from thepreceding layer by from 40% to 60% of the width of the unidirectionalfabric.
 15. The method of claim 14, further comprising applying theresin to the unidirectional fabric and bidirectional fabric prior towrapping the unidirectional fabric or bidirectional fabric around thepipe.
 16. The method of claim 15, wherein the unidirectional fabricmakes up at least 60% of the total layers of fabric at the left edgesection and makes up at least 60% of the total layers of fabric at theright edge section, and wherein the bidirectional fabric makes up atleast 20% of the total layers of fabric at the left edge section andmakes up at least 20% of the total layers of fabric at the right edgesection.
 17. The method of claim 16, wherein the unidirectional fabricmakes up at least 75% of the total layers of fabric at the centersection, wherein the unidirectional fabric makes up at least 65% of thetotal layers of fabric at the left edge section and makes up at least65% of the total layers of fabric at the right edge section, and whereinthe bidirectional fabric makes up at least 30% of the total layers offabric at the left edge section and makes up at least 30% of the totallayers of fabric at the right edge section.
 18. The method of claim 17,wherein the unidirectional fabric makes up at least 80% of the totallayers of fabric at the center section.
 19. The method of claim 17,wherein the unidirectional fabric is composed of high-performance fibersand conventional fibers with the high-performance fibers oriented in the90° direction and the conventional fibers oriented in the 0° direction,and wherein the conventional fibers are stitched to the high-performancefibers thus holding them in the 90° direction.
 20. The method of claim19, wherein the high-performance fibers have a Young's modulus of atleast 100 GPa and a tensile strength of at least 1300 MPa based on afiber diameter of 8 μm to 20 μm.
 21. The method of claim 20, wherein theconventional fibers have a Young's modulus of less than 50 GPa and atensile strength of less than 1100 MPa based on a fiber diameter of from8 μm to 20 μm.
 22. The method of claim 1, wherein the bidirectionalfabric has a length, a width, a 0° direction corresponding to the lengthof the bidirectional fabric and a 90° direction corresponding to thewidth of the bidirectional fabric, and wherein the bidirectional fabrichas from 35% to 75% of its fiber running in the 0° direction of thebidirectional fabric and 35% to 75% of its fiber running in the 90°direction of the bidirectional fabric.